The demand for compact imaging lens assembly grows in recent years with the increasing popularity of portable electronic products with photographing function. The sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor. As the advanced semiconductor manufacturing technology has allowed the pixel size of the sensors to be reduced, the compact imaging lens assemblies are gradually adopted in high pixel count cameras, which brings a stringent requirement on the image quality of the compact lens assemblies as well as requirement on precision manufacturing. These requirements usually lower the yield rate and result a higher cost; therefore, a lens system structure which is less sensitive to variations of the manufacturing process is needed.
The traditional compact imaging lens system equipped on a portable electronic device usually comprises three lenses; for example, U.S. Pat. No. 7,564,635 discloses a lens system comprising three lenses with positive refractive power; however, the conventional three-lens configuration can't meet the image quality requirement today. US Publication No. 2012/0099009 discloses a lens system having a four-lens configuration, though the image quality of this lens system is improved, however, the positive refractive powers in this design are not distributed in a balanced manner, and this lens system includes a lens element with negative refractive power, which leads to the result that the total track length of this lens system can't be reduced effectively and limits its application in compact electronic devices.
On the other hand, because of its advantages of being not interfered by visible light and being not perceived by naked eyes, infrared has been integrated with electronic technologies to develop various electronic products, such as remote control devices, infrared monitors and infrared detector systems. The emerging motion capture technology applied in smart TV or motion sensing games which captures and recognizes the user's motion by an infrared camera expands the application of compact imaging lens in infrared wavelength range. In view of this, the industry needs a lens system structure which has higher tolerance on variations of the manufacturing process and therefore a higher yield rate; furthermore, the lens system structure can suffice the needs of ordinary photography and infrared applications.